--- a/unix/Makefile.linux
+++ b/unix/Makefile.linux
@@ -5,8 +5,8 @@
 # 1) System specific additional libraries, include paths, etc
 #    (Where to find X11 libraries, etc)
 #
-SYSTEM_INCLUDES = -I/usr/X11R6/include 
-SYSTEM_LDFLAGS = -L/usr/X11R6/lib 
+SYSTEM_INCLUDES ?= -I/usr/X11R6/include 
+SYSTEM_LDFLAGS ?= -L/usr/X11R6/lib 
 SYSTEM_LIBS = -ldl -lpthread
 
 # 2) System specific capabilities
@@ -39,8 +39,8 @@ SYSTEM_HAVES = -DLINUX -DHAVE_PSELECT -D
 -DHAVE_ASSERT $(NETSEC)
 
 SYSTEM = linux
-CC = g++
-RANLIB = ranlib
-AR = ar
+CC ?= g++
+RANLIB ?= ranlib
+AR ?= ar
 
 include Makefile.common